Image analysis – Image enhancement or restoration – Intensity – brightness – contrast – or shading correction
Patent
1993-06-01
1997-04-15
Boudreau, Leo
Image analysis
Image enhancement or restoration
Intensity, brightness, contrast, or shading correction
382108, 348251, G06K 940
Patent
active
056218249
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a shading correction (compensation) method, and an apparatus therefor, in which effects ascribed to lighting irregularity, the shadows of an object, etc., are eliminated. More particularly, the invention relates to a shading correction (compensation) method, and an apparatus therefor, ideal for columnar objects such as circular cylinders, circular columns or prisms.
BACKGROUND ART
There are many cases in which shading processing, which is for eliminating a non-uniformity in brightness as caused by the lighting irregularity of a lighting device or distortion of a camera lens, is required as pre-processing for the reading of characters or for the recognition of other objects.
In conventional shading processing, a solid white reference paper having a uniform reflectivity is imaged and the resulting image is adopted as a shading pattern. When an object is imaged, a prescribed arithmetic operation (such as subtraction or division) is performed between image data indicative of the object and image data representing the shading pattern. Image data subjected to a shading correction by this operation is obtained.
With this conventional shading method, however, it is required that the reference paper be prepared in advance. Further, in a case where the object is a solid figure, such as a circular cylinder, the amount of light incident upon the image pick-up device differs depending upon the location of the object. This light is part of the illuminating light that has been reflected by the object. More specifically, most of the light reflected from the portion of the object facing the image pick-up device impinges upon the image pick-up device. However, at the side faces of the object or portions in the vicinity thereof, the illuminating light is not reflected toward the position of the image pick-up device. Most of this reflected light does not impinge upon the image pick-up device. Consequently, when an object having such a solid shape is photographed, the photographic image develops a shadow (meaning a portion that is comparatively dark). It is difficult to prevent such a variance in light and darkness with the conventional method using the aforesaid reference paper.
An object of the present invention is to provide a shading correction method, and an apparatus therefor, whereby it is possible to eliminate the effects of shadows, which are caused by solid shapes, without using a reference paper or the like.
Another object of the present invention is to make possible a correct shading correction even in a case where the position of an object to be imaged in the visual field of a camera has shifted from a reference position.
DISCLOSURE OF THE INVENTION
A shading correction method and apparatus according to a first aspect of the present invention are as follows:
A shading correction method according to a first aspect of the present invention comprises steps of imaging a columnar object using an image pick-up device to obtain image data representing the object, displaying the image represented by the image data on a display unit, designating, on the image displayed by the display unit, a sample location in linear form in a direction perpendicularly intersecting a longitudinal direction of the object, creating two-dimensional shading-pattern data by continuously arranging a density-level distribution, which is identical with that along the designated linear sample location, in the longitudinal direction of the object, and performing a shading correction of the image data representing the object by using the shading-pattern data.
In an embodiment of the invention, the sample location is designated by the position of a line drawn on the image or by a slender window displayed on the image.
The shading correction method according to the first aspect of the invention can also be expressed as comprising steps of extracting, from image data obtained by imaging an object, image data of a sample location designated in linear form on a displayed image of the object, creating two-di
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Awano Naoshi
Ijiri Takashi
Masaki Toshimichi
Matsumoto Toshihiko
Motooka Osamu
Boudreau Leo
Kelley Chris
Omron Corporation
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